1. Field of the Invention
The present invention is in the field of an apparatus for applying thin layers onto a substrate wherein the substrate is periodically conveyed between at least two evacuatable chambers in which an inert gas can be provided, with control means for preventing contamination between chambers.
2. DESCRIPTION OF THE PRIOR ART
In cathode atomization which is also referred to as cathode sputtering, atoms are stripped from a cathode in a vacuum by means of ions of an inert gas which are formed in a gas discharge. The atoms then deposit on a substrate located in opposed relation to the cathode. In a modification of this sputtering technique, in what is referred to as reactive sputtering, it is not the source material itself which is deposited but a compound which arises by reaction with a reactive gas.
Thin layers of titanium, titanium nitride, and aluminum are successively sputtered onto individual wafers in various chambers for the formation of contacts and interconnects in the manufacture of transistor megabit memories. Argon is normally introduced into the appropriate chambers as an inert gas in the sputtering of titanium and of aluminum, and nitrogen is used as a reactive gas so as to provide a reactive gas which is introduced into a treating chamber in the reactive sputtering of the titanium nitride. A feed of inert gas and of reactive gas occurs by means of a shut-off valve and a flow governor or regulator. In order to prevent a cross-contamination between the individual chambers of the sputtering apparatus due to the presence of the reactive gas, the reactive gas must be pumped off before the wafer transport takes place between chambers, and, in particular, before the slot valves between adjoining chambers are opened for the passage of wafers between chambers. When the next wafer is to be subsequently processed, a new supply of reactive gas must be introduced into the chamber in addition to the inert gas, and the gas flows must be stabilized. In view of the high vacuum of about 10.sup.-4 to 10.sup.-5 Pa required in the chamber, pumping the old reactive gas or the reaction gas mixture requires a relatively long time of several minutes. The admission and stabilization of the new reactive gas likewise requires an excessively long time in view of the required throughput.